Stuck Fan Clutch

[mgFray]

Yep, I was thinking the exact same thing. The only reason why I mentioned the flow being low was because without knowing the internal design of the cadillac valve, low flow out of the bleeder COULD be an indication of low pressure. I suppose that depends on how much restriction there is, since flow is determined by pressure and restrictions.

Either way, I dont have all of the information until I measure it, so thats next.

Mine does work, and the flow is VERY low. So I think finding a gauge is the best way to check on the pressure part.

 

[papakb]

Just out of curiosity how's your power steering? The pressure that cycles the fan comes from the power steering pump and if that's failing it may not be producing enough pressure the cycle the fan clutch but a gauge on the output of the Cadillac valve will answer that question.

mgFray, the fan clutch is a closed system it's either pressurized or isn't, there's no flow happening.

 

[Autonomy_Lost]

Just out of curiosity how's your power steering? The pressure that cycles the fan comes from the power steering pump and if that's failing it may not be producing enough pressure the cycle the fan clutch but a gauge on the output of the Cadillac valve will answer that question.

mgFray, the fan clutch is a closed system it's either pressurized or isn't, there's no flow happening.

Power steering works fine.

I think mgFray is refering to the bleeder valve (only some trucks have this). You can open it and observe fluid flowing out when the cadillac valve is open.

 

[Autonomy_Lost]

Update:

Let me start by saying how I am determining whether the fan is on. With the truck running, I'm trying to stop the blades with a rolled up magazine. This will become relavent in a minute.

My cadillac valve is putting out 160PSI.

The fan clutch disengages with around 120PSI of air (engine is off when I'm testing this). The clutch moves in/out about a 1/4 inch, and I can move the blades by hand. However, there is still a LITTLE bit of resistance (when I spin it, as soon as my hand leaves, it stops).

With everything back together, I realize that the fan clutch IS disengaging, but for some reason its still tight enough that I cant stop it with a stack of papers.

Maybe everything is fine? Anyone have insight on this?

 

[Retiredwarhorses]

Update:

Let me start by saying how I am determining whether the fan is on. With the truck running, I'm trying to stop the blades with a rolled up magazine. This will become relavent in a minute.

My cadillac valve is putting out 160PSI.

The fan clutch disengages with around 120PSI of air (engine is off when I'm testing this). The clutch moves in/out about a 1/4 inch, and I can move the blades by hand. However, there is still a LITTLE bit of resistance (when I spin it, as soon as my hand leaves, it stops).

With everything back together, I realize that the fan clutch IS disengaging, but for some reason its still tight enough that I cant stop it with a stack of papers.

Maybe everything is fine? Anyone have insight on this?

my insight is that’s not how you test to see if the fan blade is unlocked…
either Visually observe the engagement and disengagement of the fan, or raise the Rpm’s to say 1500rpm and unplug the TDM, you will
hear The difference of engaged and disengaged quite effortlessly, even more so if your driving down the road under load.

 

[Autonomy_Lost]

my insight is that’s not how you test to see if the fan blade is unlocked…
either Visually observe the engagement and disengagement of the fan, or raise the Rpm’s to say 1500rpm and unplug the TDM, you will
hear The difference of engaged and disengaged quite effortlessly, even more so if your driving down the road under load.

Thanks, thats helpful. The newspaper test is a common way to diagnose fan clutches on civilian vehicles, but obviously the hmmwv is a different beast.

So at the end of the day, I spent about 5 hours and $100 worth of parts diagnosing a problem that didn't exist, lol.

But hey, I have come out of it with a better understanding of how this machine works!

 

[Milcommoguy]

Update:

Let me start by saying how I am determining whether the fan is on. With the truck running, I'm trying to stop the blades with a rolled up magazine. This will become relavent in a minute.

My cadillac valve is putting out 160PSI.

The fan clutch disengages with around 120PSI of air (engine is off when I'm testing this). The clutch moves in/out about a 1/4 inch, and I can move the blades by hand. However, there is still a LITTLE bit of resistance (when I spin it, as soon as my hand leaves, it stops).

With everything back together, I realize that the fan clutch IS disengaging, but for some reason its still tight enough that I cant stop it with a stack of papers.

Maybe everything is fine? Anyone have insight on this?

If you're going to grind up a magazine in the fan... at least remove the center fold.

Show something for your work, CAMO

 

[Autonomy_Lost]

Part of my problem is that I'm still waiting on the stupid SF97, so I cant drive the damn thing on the road. So I'm diagnosing all this stuff in my driveway. I'm sure if I was driving it around I'd realize that everything is okay.

 

[mgFray]

Just out of curiosity how's your power steering? The pressure that cycles the fan comes from the power steering pump and if that's failing it may not be producing enough pressure the cycle the fan clutch but a gauge on the output of the Cadillac valve will answer that question.

mgFray, the fan clutch is a closed system it's either pressurized or isn't, there's no flow happening.

When replacing the old hose, there needs to be some 'flow' to purge the system of air. Thus it exists, just VERY slow. My take is the valve is good at introducing pressure (and letting it bleed off) but isn't really a substitute for redirecting fluid flow.

 

[Coug]

When replacing the old hose, there needs to be some 'flow' to purge the system of air. Thus it exists, just VERY slow. My take is the valve is good at introducing pressure (and letting it bleed off) but isn't really a substitute for redirecting fluid flow.

might be a little confusion here, but the fan clutch is a dead end system. It doesn't have to be purged of air to function.
Over time the air does get purged, because the fluid comes in and compresses the air, and the air gradually makes it's way up the hose to the cadillac valve as the fan clutch engages/disengages.

So the fan clutch system doesn't have a "flow" per se, just pressure in and pressure out with the amount of fluid needed to move the clutch being the entire extent of the flow amount.

 

[Mogman]

When replacing the old hose, there needs to be some 'flow' to purge the system of air. Thus it exists, just VERY slow. My take is the valve is good at introducing pressure (and letting it bleed off) but isn't really a substitute for redirecting fluid flow.

I wonder what changed? none of the early trucks had bleeder valves, I have replaced hoses and never had a reason to bleed the system.

 

[Mogman]

might be a little confusion here, but the fan clutch is a dead end system. It doesn't have to be purged of air to function.
Over time the air does get purged, because the fluid comes in and compresses the air, and the air gradually makes it's way up the hose to the cadillac valve as the fan clutch engages/disengages.

So the fan clutch system doesn't have a "flow" per se, just pressure in and pressure out with the amount of fluid needed to move the clutch being the entire extent of the flow amount.

We posted at almost the exact same time

 

[Mogman]

What everyone is calling a bleeder?, is it possible it is actually a diag. port to check the pressure?, As Coug said dead head systems usually bleed themselves.

 

[Autonomy_Lost]

What everyone is calling a bleeder?, is it possible it is actually a diag. port to check the pressure, As Coug said dead head systems usually bleed themselves

Its literally a brake bleeder valve, I actually replaced mine with a generic one from the parts store. I suppose you could hook something up to meausure it?

 

[Mogman]

Its literally a brake bleeder valve, I actually replaced mine with a generic one from the parts store. I suppose you could hook something up to meausure it?

OK, thanks!! maybe those were installed when they went to the coupling at the clutch, to remove any residual pressure which would prevent seperating the coupling.

 

[Autonomy_Lost]

OK, thanks!! maybe those were installed when they went to the coupling at the clutch, to remove any residual pressure which would prevent seperating the coupling.

Its actually installed on a tee on the output of the cadillac valve, so if you really wanted one for some reason you could retrofit it. But its a specialty tee since the top port is milled to be a seat for the bleeder (not standard NPT threads).

A possible reason they installed it is simply because its the highest point in the pressurized system, so it would be a good place to bleed the whole system assuming the cadillac valve is open.

 

[Mogman]

Its actually installed on a tee on the output of the cadillac valve, so if you really wanted one for some reason you could retrofit it. But its a specialty tee since the top port is milled to be a seat for the bleeder (not standard NPT threads).

A possible reason they installed it is simply because its the highest point in the pressurized system, so it would be a good place to bleed the whole system assuming the cadillac valve is open.

I will bet it was to remove any residual pressure which would keep you from separating the coupling, any air trapped at the cadillac valve would easily be pushed through the valve as it activated and de activated under normal operation, would be the least necessary location for a "trapped air" bleeder.
EDIT, it would still be considered a bleeder, a pressure bleeder.

 

[sue]

Th

I will bet it was to remove any residual pressure which would keep you from separating the coupling, any air trapped at the cadillac valve would easily be pushed through the valve as it activated and de activated under normal operation, would be the least necessary location for a "trapped air" bleeder.
EDIT, it would still be considered a bleeder, a pressure bleeder.

The amazing thing is when (and if) you take your fan
“Clutch” apart there is only one tiny O ring keeping it from leaking!!! As much wear and abuse it gets and that little O ring does a heck of a job.
And yes some will say I’m smoking crack but you can
Twist, push, pull to get the fan out without pulling the shroud or radiator.

 

[papakb]

A few months back I did the fan clutch / water pump / hoses replacement and pulled the radiator stack out as a unit. What I learned when reinstalling it is that you can't just let it sit on the frame when you bolt it back in. I did that and the fan kept touching the shroud. The other thing I learned was that after reconnecting the line to the Cadillac valve I never had to do any bleeding. It seemed to self purge. I was worried about this and thought about a bleeder install but found it wasn't necessary. One last thing I did was to scrap the barbed fittings and went with Aeroquip on all the connections.

 

[jmenende]

Th

The amazing thing is when (and if) you take your fan
“Clutch” apart there is only one tiny O ring keeping it from leaking!!! As much wear and abuse it gets and that little O ring does a heck of a job.
And yes some will say I’m smoking crack but you can
Twist, push, pull to get the fan out without pulling the shroud or radiator.

Howdy, my A2 was plundered and came with an old v belt fan that caused overheating. I am currently replacing the fan the hard way and am unable to remove the fan clutch which works properly I might add. The 1/2 nut keeps on spinning even when I apply the 90 psi to the line to engage the clutch. My shroud was previously cut so removing the fan w/o taking the radiator out seems doable but that darn clutch wont budge. Any pointers are appreciated.